High pressure pulsed gas sources derived by electrothermal techniques are disclosed, for example, in commonly assigned U.S. Pat. Nos. 4,590,842, 4,715,261, 4,974,487 and 5,012,719. In these prior art pulsed gas sources, a capillary discharge is formed in a passage between a pair of spaced electrodes at opposite ends of a dielectric tube, preferably formed of polyethylene. In response to a discharge voltage between the electrodes, a high pressure, high temperature plasma fills the passage, causing material to be ablated from the dielectric wall. High temperature, high pressure plasma gas flows longitudinally of the discharge and the passage through an aperture defined by an electrode at one end of the passage. The gas flowing longitudinally from the passage through the aperture produces a high pressure, high velocity gas jet that can accelerate a projectile to a high velocity. In the '487 patent, the high pressure, high temperature plasma interacts with a propellant mass to produce a high temperature propellant. In the '719 patent, hydrogen is produced by interacting the plasma flowing through the orifice with a metal hydride and some other material to produce high pressure hydrogen. The plasma is cooled by interacting with a cooling agent, for example water, while an exothermal chemical reaction is occurring.
In the '487 patent, the pressure acting on the rear of a projectile is maintained substantially constant while the projectile is accelerated through a barrel bore even though the volume of the barrel bore between the high pressure source outlet orifice and the projectile increases. Such a result is attained by increasing the electric power applied to the capillary discharge in a substantially linear manner as a function of time.
In still a further high pressure pulsed gas source disclosed in commonly assigned U.S. Pat. No. 5,072,647, a high pressure plasma discharge is established between a pair of axially displaced electrodes. The pressure of the plasma in the discharge is sufficient to accelerate a projectile in a gun barrel bore. The plasma is established in a walled structure confining the discharge and having openings through which the plasma flows transversely of the discharge. A chamber surrounding the wall includes a slurry of water and metal particles to produce high pressure hydrogen gas that flows longitudinally of the discharge against the rear of a projectile. To maintain the pressure of the hydrogen gas acting against the projectile relatively constant as the projectile is accelerated down the barrel, electric power applied to the discharge increases substantially linearly as a function of time.
Some concepts employed in the '647 patent have been incorporated into the copending, commonly assigned application Ser. No. 08/238,433, filed May 5, 1994. In this copending application, a structure establishes at least several axial electrical discharges across axial gaps behind an outlet of a high pressure pulsed gas source, particularly adapted for driving a projectile. The discharges cause plasma to flow with components at right angles to the axial discharges. A conventional propellant mass, e.g. gunpowder, or a hydrogen producing mass, as disclosed in the '647 patent, is positioned to be responsive to the plasma flow resulting from the discharges. In response to the plasma resulting from the discharges being incident on the propellant mass, a high pressure gas pulse is produced.
Those working in the art have recognized that it is desirable for plasma accelerating a projectile to have a maximum amount of energy close to the base, i.e., rear, of the projectile. Hence, after a projectile is initially accelerated, it is desirable for the power close to the projectile, at the front of a plasma source, to be greater than the power at the rear of the plasma source. However, a problem in producing a plasma with such a power or energy distribution is that pressure waves have a tendency to be produced in the plasma source. The pressure waves from a high pressure plasma source, such as derived from a highly energetic electric power supply (having millions of Joules of energy), can be destructive of a projectile launcher including such a high pressure source. It is, therefore, desirable for a high pressure plasma source having at least several axial electrical discharges to initially produce plasma having about the same power over all of the gaps. After the projectile has moved away from its initial position, it is then desirable for the power applied to the plasma close to the projectile to exceed the power of the plasma farther from the projectile.
A problem with the aforementioned types of devices is that the plasma has as tendency to flow through a plasma confining structure to an electrode needed to establish the axial electrical discharges; the electrode must be at a high voltage relative to metal parts close to it. If the plasma has a high temperature at the time it is incident on the electrode, many charge carriers are incident on the electrode, causing a low impedance electric path to subsist between the electrode and the metal parts. The electric discharges thus have a tendency to be quenched. To overcome this problem in the past, it has been the general practice to design the structure so the electrode is a great distance from the discharge structure. Such an arrangement enables the high temperature of the plasma to be largely dissipated to reduce the number of plasma charge carriers incident on the electrode. However, such a lengthy structure is not conducive to optimum design of cartridges including projectiles adapted to be loaded into military hardware.
It is, accordingly, an object of the present invention to provide a new and improved electrothermal apparatus for deriving a high pressure gas pulse, particularly adapted to drive a projectile in a gun bore.
Another object of the invention is to provide a new and improved cartridge including a projectile and an electrothermal structure for driving the projectile to high speeds in a gun barrel.
An additional object of the invention is to provide a new and improved electrothermal apparatus including at least several axially displaced gaps for deriving a plasma that flows radially with respect to a structure including the axial gaps.
A further object of the invention is to provide a new and improved cartridge including a projectile attached to a structure for deriving at least several axially spaced plasma jets that flow into a propellant mass that is radially displaced from the structure.
An added object of the invention is to provide a new and improved high pressure pulsed gas source, particularly adapted for accelerating a projectile along a gun barrel, and including at least several axial gaps for providing at least several axial electrical discharges behind an outlet of the source to apply greater power to the plasma via gaps close to the outlet than the power applied to the plasma via the gaps farther from the outlet, after the pulse is initially formed and is still being derived.
Another object of the invention is to provide a new and improved high pressure pulsed gas source particularly adapted for accelerating a projectile along a gun barrel, including a structure for establishing at least several axial discharges in axial gaps behind an outlet of the source where the projectile is initially located, wherein the plasma, as initially produced, has substantially the same pressure in all of the gaps and produces sufficient pressure to accelerate the projectile away from the initial position thereof and after the projectile moves away from its initial position and is in the barrel, the power applied to plasma in gaps close to the projectile is greater than the power applied to plasma in gaps farther from the projectile.
A further object of the invention is to provide a new and improved cartridge including a projectile and a propelling structure for the projectile, wherein the propelling structure establishes at least several axial electrical discharges in corresponding axial gaps, which discharges result in a high pressure gas pulse that applies a greater amount of plasma to a projectile traversing a barrel via gaps close to the projectile than is applied via gaps farther from the projectile.
An additional object of the invention is to provide a new and improved cartridge including a projectile and a structure for establishing at least several axial electrical discharges in axial gaps behind the projectile, wherein plasma resulting from the discharges is incident on a propellant mass and the axial gaps are arranged so that (a) when the plasma is initially produced the power applied to the plasma is substantially the same over the several discharges and has sufficient pressure to accelerate the projectile away from an initial position thereof, without destroying the structural integrity of the projectile launcher, and (b) after the projectile has moved away from its initial position the power applied to the plasma via gaps close to the projectile is greater than the power applied to the plasma via gaps farther from the outlet.
It is a further object of the invention to provide a new and improved structure for overcoming the tendency for high temperature plasma to be coupled from an electrical discharge structure via a plasma containment structure to an electrode designed to be maintained at a voltage quite different from that of the discharge structure.
Still an additional object of the invention is to provide a new and improved relatively short structure for overcoming the tendency for high temperature plasma to be coupled from a plasma generating electrical discharge structure, wherein the plasma is prevented from reaching an electrode for establishing the discharge.